Page Table Entry (Level 2 Descriptor); Level 2 Section Descriptor - Texas Instruments OMAP5910 Technical Reference Manual

2.7.6.5 Level 2 Descriptor
Figure 2–15. Page Table Entry (Level 2 Descriptor)
31
Large Page Base Address
Small Page Base Address
Tiny Page Base Address
Table 2–21. Level 2 Section Descriptor
Bit Name
31–10 PG_BASE
11–4 AP
3 C
2 B
The level 1 fetch, when returning a coarse or fine page table descriptor, pro-
vides the base address of the page table to be used. The page table is then
accessed, and a level 2 descriptor is returned. This descriptor defines a tiny,
small, or large page access. Figure 2–15 shows the format of level 2 descrip-
tors.
20 19 16 15
Coarse page tables have 256 entries, and each entry describes 4K bytes.
These entries provide a base address for either small or large pages. Large
page descriptors must be repeated in 16 consecutive entries.
Fine page tables have 1024 entries, and each entry describes 1K byte. These
entries provide a base address for tiny, small, or large pages. Small page
descriptors must be repeated in four consecutive entries. Large page descrip-
tors must be repeated in 64 consecutive entries.
The two least significant bits indicate the page size and validity and are
interpreted as follows.
Function
Bits 31–10 (tiny pages), bits 31–12 (small pages), or bits 31–16 (large pages) are
used to form the corresponding bits of the physical address—the physical page
number. The page index is derived from the virtual address.
Specify the access permissions (ap3-ap0) for the four subpages within large and
small pages. Tiny pages do not have subpages and bits 5-4 specify the access
permission (see Table 2–24). For large pages, bits 15-12 SBZ.
Cacheable (C_MMU): indicates that data or instructions at this address are
placed in the cache if the cache is enabled.
Indicates that data writes at this address are buffered if the write buffer is
enabled.
MPU Memory Management Unit
12 11 10 9 8 7 6 5 4 3 2 1
ap3 ap2 ap1 ap0
ap3 ap2 ap1 ap0
ap
MPU Subsystem
0
0 0 Fault
C B 0 1 Large Page
C B 1 0 Small Page
C B 1 1 Tiny Page
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